Method and system for providing operations, administration, and maintenance capabilities in packet over optics networks

ABSTRACT

A method for conveying management information across a network. The method includes receiving an Ethernet packet at a network element and modifying the packet by inserting a header in place of some or all of an unused portion of a preamble within the packet. The header is configured to provide support for network management. The method further includes transmitting the modified packet from the network element. The method may also include examining and updating the header at intermediate network elements and examining and replacing the header with the preamble at an egress network element.

BACKGROUND OF THE INVENTION

The present invention relates generally to digital communicationnetworks, and more specifically, to packet over optics networks.

In the early days of fiber optics, every telephone company had its ownproprietary optical Time Division Multiplexing (TDM) protocol. In 1985the telecommunications industry began working on a standard calledSONET. This work resulted in a SONET standard in 1989. The advent oftechnologies such as Asynchronous Transfer Mode (ATM) over SONET anddirect mapping of IP over SONET frames has extended the useful life ofthis technology. Packet over SONET has recently been used to support thedeployment of IP-based video and voice applications. Packet over SONETplaces the IP layer directly above the SONET layer and eliminates theoverhead needed to run IP over ATM over SONET (FIG. 1A). FIG. 1Billustrates conventional Ethernet over SONET. Virtually all the longdistance telephone traffic in the United States and elsewhere now usestrunks running SONET in the physical layer.

SONET and SDH are a set of related standards for synchronous datatransmission over fiber optic networks. SONET is short for SynchronousOptical Network and SDH is an acronym for Synchronous Digital Hierarchy.SONET is the United States version of the standard published by theAmerican National Standards Institute (ANSI). SDH is the internationalversion of the standard published by the InternationalTelecommunications Union (ITU).

SONET/SDH is currently used in wide area networks (WAN) and metropolitanarea networks (MAN). A SONET system consists of switches, multiplexers,and repeaters, all connected by fiber. The connection between a sourceand destination is called a path. The basic SONET frame is a block of810 bytes transmitted every 125 μsec. Since SONET is synchronous, framesare emitted whether or not there is any useful data to send. The firstthree columns of each frame are reserved for system managementinformation. The first three rows contain section overhead and the nextsix contain line overhead. A section is a fiber going directly from anydevice to any other device, with nothing in between. A line is runbetween two multiplexers. The section overhead is generated and checkedat the start and end of each section, whereas the line overhead isgenerated and checked at the start and end of each line. The firstcolumn of user data (called the synchronous payload envelope (SPE)) isthe path overhead (i.e., header for the end-to-end path sublayerprotocol). The section, line, and path overheads contain a profusion ofbytes used for operations, administration, maintenance, and provisioning(OAM&P). Since each byte occurs 8000 times per second, it represents aPCM (pulse code modulation) channel. Three of these are used to providevoice channels for section, line, and path maintenance personnel. Otherbytes are used for framing, parity, error monitoring, IDs, clocking,synchronization, and other functions.

SONET/SDH and optical fiber have emerged as significant technologies forbuilding large scale, high speed, Internet Protocol (IP) based networks.However, it is desired to eliminate the intervening SONET/SDH layer infuture packet over optics networks for cost efficiency, ease ofmanagement, and bandwidth efficiency.

One standard that describes the interconnection of computer devices inlocal area network (LAN) communication is IEEE (Institute of Electricaland Electronic Engineers) standard 802.3, commonly referred to asEthernet (also adopted as International Standard ISO/IEC 8802-3). TheEthernet system includes an Ethernet frame that consists of astandardized set of bits used to carry data over the system. The fieldsof an Ethernet packet (also referred to as an Ethernet frame) includeaddress fields, a variable size data field that carries from 46 to 1500bytes of data, and an error checking field that checks the integrity ofbits in the frame to make sure that the frame has arrived intact. TheEthernet frame encapsulates payload data by adding a 14 byte headerbefore the data and appending a 4-byte (32-bit) cyclic redundancy check(CRC) after the data. The entire frame is preceded by a small idleperiod (the minimum inter-frame gap, 9.6 microseconds) and an 8 bytepreamble.

In the case of 10 Mbps and 100 Mbps Ethernet, the preamble is typicallyused to allow time for the receiver in each node to achieve lock of thereceiver Digital Phase Lock Loop which is used to synchronize thereceive data clock to the transmit data clock. At the point when thefirst bit of the preamble is received, each receiver may be in anarbitrary state (i.e., have an arbitrary phase for its lock clock).During the course of the preamble it learns the correct phase, but indoing so, it may miss (or gain) a number of bits. A special pattern,known as the start of frame delimiter, is used in conventional systemsto mark the last two bits of the preamble. When this is received, theEthernet receive interface starts collecting bits for processing by theMAC (medium access control) layer.

For 1 Gbps Ethernet (IEEE 802.3a), 8b/10b transmission code is used.Synchronization and code group alignment makes use of the comma controlcharacter. The preamble (including the start of frame field) has alength of eight bytes and has been retained only for backwardcompatibility. The preamble (excluding the start of frame field) isthus, for the most part, extra overhead which is not fully utilized.

Ethernet is typically not used in WAN applications since it does notprovide operations, administration, maintenance, and provisioningcapabilities. It would be desirable to modify the standard Ethernetpacket to provide OAM&P capabilities and eliminate the need for theSONET/SDH layer in packet over optics networks.

SUMMARY OF THE INVENTION

Methods and systems for providing operations, administration, andmaintenance capabilities in packet over optics networks are disclosed.

A method for conveying network management information across a networkgenerally comprises receiving an Ethernet packet at a network elementand modifying the Ethernet packet by inserting a header in place of apreamble within the packet. The header provides support for networkmanagement. The method further includes transmitting the modified packetfrom the network element.

The method may further include reading and modifying the managementinformation at transit nodes and replacing the header with a standardpreamble at an egress node. The network management may includeoperations, administration, maintenance, and provisioning (OAM&P), forexample, The header preferably includes the same number or a fewernumber of bytes than the preamble of the Ethernet packet so that a sizeof the packet is not increased when the preamble is replaced by theheader. The header is preferably inserted at an edge of the managednetwork. The header is removed and replaced with the preamble at anegress boundary of the managed network. The header may include asubinterface identifier that identifies the originating port of thepacket so that packet streams can be multiplexed at one node within thenetwork and demultiplexed at another node within the network. Idlepackets may be inserted into the packet stream at locations where nodata is received by the network element so that the OAM&P information inthe headers may be carried across the network even in the absence ofuser data frames.

A system for supporting network management includes a network elementgenerally comprising a port controller operable to receive a packet andmodify the packet by inserting a header in place of a preamble withinthe packet. The header is configured to provide support for networkmanagement. The network element further comprises a network elementcontroller coupled to the port controller and operable to generate andconsume network management information.

The port controller may include an optical to electrical converter, aCDL handler, and a crossconnect. The handler may be dedicated hardware,microcode, software, or photonic (optical) logic, for example.

The system may further include a second network element positioned at anegress boundary of the network and operable to replace the header withthe preamble. A plurality of transit network elements may be positionedwithin the network to connect the ingress network element with theegress network element. The transit element is configured to receive themodified packet, modify the header, and forward the packet.

In another aspect of the invention, a system generally comprises ahandler operable to remove a preamble from an Ethernet packet and inserta header. The header may include an operations, administration, andmaintenance field, a message channel, an application specific field, anda header error detection field.

In yet another aspect of the invention, a computer program product forsupporting network management generally comprises code that receives anEthernet packet and code that modifies the Ethernet packet by insertinga header in place of a preamble within the packet. The header providessupport for network management. The product further includes code thattransmits the modified packet from a network element and acomputer-readable storage medium for storing the codes.

A system of the present invention generally comprises a processor thatexecutes a program for modifying an Ethernet packet to provide OAMcapabilities. The program includes code that receives an Ethernetpacket, code that modifies the Ethernet packet by inserting a header inplace of a preamble within the packet, code that transmits the modifiedpacket over a path within the network, and a computer-readable storagemedium having the program stored thereon.

In another aspect of the invention, a system generally comprises aprocessor operable to remove a preamble from an Ethernet packet andinsert a header into the packet. The header includes an operations,administration, and maintenance field, a message channel, an applicationspecific field, and a header error protection field.

In yet another aspect of the invention, a system for supporting networkmanagement generally comprises a processor operable to wrap a digitalwrapper around a data link layer. The digital wrapper comprises anoperations, administration, and maintenance field, a message channel, anapplication specific field, and an error protection field covering thedigital wrapper.

A system for conveying network management information across a networkgenerally comprises means for receiving a packet at a network element,means for modifying a preamble of the packet to support networkmanagement, and means for transmitting the modified packet.

The above is a brief description of some deficiencies in the prior artand advantages of the present invention. Other features, advantages, andembodiments of the invention will be apparent to those skilled in theart from the following description, drawings, and claims.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1A is a diagram illustrating layers of a prior art packet overoptics network utilizing SONET.

FIG. 1B is a diagram illustrating layers of a prior art Ethernet overSONET system.

FIG. 2 is a diagram illustrating the relationship between a convergeddata link layer of the present invention and an IP and optical layer.

FIG. 3A is a diagram illustrating edge and transit network elementswithin a network.

FIG. 3B is a diagram of one of the network elements of FIG. 3A showingadditional detail.

FIG. 3C is a diagram illustrating an ingress port controller of thenetwork element of FIG. 3B.

FIG. 3D is a diagram illustrating an egress port controller of thenetwork element of FIG. 3B.

FIG. 4 is a system block diagram of a computer system that can beutilized to execute software of an embodiment of the present invention.

FIG. 5 is a diagram illustrating a standard Ethernet packet.

FIG. 6 is a diagram of the Ethernet packet of FIG. 6 modified to includea converged data link header of the present invention.

FIG. 7 is a schematic illustrating two network elements connected to anetwork management station.

FIG. 8 is a schematic illustrating a plurality of network elementsconnected to a network management station.

FIG. 9A is a diagram illustrating a CDL header configured to supportmultiplexing of packet streams.

FIG. 9B is a schematic illustrating multiplexing of packets using theCDL header of FIG. 9A.

FIG. 10 is a diagram of an exemplary shift register used to calculate aheader CRC of the converged data link.

FIG. 11A is a schematic illustrating data packets traveling along apath, each packet containing data.

FIG. 11B is a schematic illustrating the path of FIG. 11A with an idlepacket inserted between the data packets at a location where no data isbeing transmitted.

FIG. 12 is a schematic illustrating an optical network with networkelements located along an edge of the network for modifying Ethernetpackets as the packets enter and exit the network.

FIG. 13 is a schematic illustrating an optical network with a dual ringtopology.

FIG. 14 is a diagram illustrating a CDL header for a network having adual ring topology.

FIG. 15 is a schematic illustrating an optical network with a meshtopology.

FIG. 16A is a schematic illustrating packets received from a first pathand a redundant path at a network element.

FIG. 16B is a schematic of the network of FIG. 16A illustrating thetransmittal of packets from the network element.

FIG. 16C is a schematic illustrating an error threshold reached at thenetwork element and the element switching to the redundant data path.

FIG. 17 is a flowchart illustrating a process for receiving Ethernetpackets along an edge of an optical network and modifying the packets toadd a converged data link header.

Corresponding reference characters indicate corresponding partsthroughout the several views of the drawings.

DETAILED DESCRIPTION OF THE INVENTION

The following description is presented to enable one of ordinary skillin the art to make and use the invention. Descriptions of specificembodiments and applications are provided only as examples and variousmodifications will be readily apparent to those skilled in the art. Thegeneral principles described herein may be applied to other embodimentsand applications without departing from the scope of the invention.Thus, the present invention is not to be limited to the embodimentsshown, but is to be accorded the widest scope consistent with theprinciples and features described herein. For purpose of clarity,details relating to technical material that is known in the technicalfields related to the invention have not been described in detail.

FIG. 2 illustrates network layers in a system of the present inventionused to transport data over optical networks. The system includes aconverged data link (CDL) which replaces the SONET layer in conventionalsystems. CDL may be applied, for example, to any physical link layerthat is capable of full-duplex transmission of Ethernet packets. CDLlayer 70 operates between IP layer 76 and a physical layer of theoptical network 74. It is to be understood that other lower and higherlayers may be used without departing from the scope of the invention.

CDL enables configuration, performance, and fault management of thenetwork without the intervening SONET/SDH layer (see FIG. 1), thusreducing system costs and increasing management and bandwidthefficiencies. CDL further provides operations, administration,maintenance and provisioning (OAM&P) (or OAM, or any single feature orcombination thereof), multiplexing, and multiple qualities of service inpacket over optics networks. For example, CDL may support generalmanagement of optical networks, supervision of unused channels,provisioning of optical paths, performance monitoring of optical paths,and failure recovery. CDL also enables multiplexing of multiple logicallower speed circuits across a single optical channel including supportfor a multi-access form of statistical multiplexing appropriate to ringtopologies. It is to be understood that CDL may provide all of the abovementioned functions, only one of these functions, or any combination ofthese functions, without departing from the scope of the invention.

The method and system of the present invention are used to modify theEthernet protocol to add additional functions. As described below, astandard Ethernet packet is modified to add CDL information upontransmission, and a received CDL packet is converted to a standardEthernet packet by stripping the CDL information upon reception. Theinvention may also be implemented without having the packet pass througha device in a standard Ethernet format. An example is a computer with asingle network interface that transmits and receives CDL formattedframes on that interface.

The present invention operates in the context of a data communicationnetwork including multiple network elements. A network element may be,for example, a terminal multiplexer, an add-drop multiplexer (ADM), anoptical crossconnect (OXC), or a signal regenerator. Two terminalmultiplexers may be linked by fiber optics with or without a regeneratorto form an optical path. A regenerator may be needed when, due to a longdistance between multiplexers, the signal level in the fiber becomes toolow. The regenerator recovers timing from the received signal. An ADMmay be deployed at a terminal site or any intermediate location forconsolidating traffic from widely separated locations. Several ADMs mayalso be configured as a survivable ring. At the site of an ADM, onlythose signals that need to be accessed are dropped or inserted. Theremaining traffic continues through the network element withoutrequiring special pass through units or other signal processing. Thecrossconnect may be used to establish association between ingress andegress links, as described below. Optionally a crossconnect maydemultiplex or multiplex a signal that is a group of signals into orfrom its constituent signals and perform cross connection at thegranularity of its constituent signals.

CDL is used in the transmission of packets along an optical path (OP)across networks that are composed of network elements. FIG. 3Aillustrates an exemplary network comprising a plurality of networkelements 26, 28. An optical path may pass through any number ofintermediate network elements. The end point of a CDL optical path maybe a router or other network element if it is acting as a gateway to asection of the network which does not support CDL. For example, network22 is connected to a router or host 24. The router or host 24 sendspackets into the network 22 to a network element 26 located on an edgeof the network. The network 22 shown in FIG. 3A includes three edgenetwork elements 26 which are interconnected with transit networkelements 28 through network/node interfaces. The edge network elements26 may also receive transmissions from a user/network interface 30. Theedge network elements 26 which are positioned to receive transmissionscoming into the network (i.e., two edge network elements (ENE) on leftside of network as viewed in FIG. 3A), are referred to as ingress edgenetwork elements. The edge network element positioned to transmitpackets from the network 22 (i.e., right most ENE in FIG. 3A) isreferred to as an egress edge network element. As further describedbelow, the ingress edge network elements 26 are configured to replace apreamble in the incoming packet with the CDL header, the transit networkelements 28 are configured to modify the CDL header and forward thepacket, and the egress edge network elements are configured to replacethe CDL header in the incoming packet with the preamble.

While this invention is described with ingress transit and egressnetwork interfaces, these functions may also be combined into a singleimplementation. For example, data flows through an edge network elementmay bi-directional, in which case the same network element acts as aningress network element for frames heading into the network, and as anegress element for frames leaving the network.

The invention described herein may be implemented in dedicated hardware,microcode, software, or photonic (optical) logic. FIGS. 3B and 3Cillustrate an implementation in dedicated hardware. FIG. 3B is a diagramof one of the edge network elements 26 of FIG. 3A. The network element26 includes a plurality of port controllers 32, crossconnect 34, andnetwork element controller 36. The port controllers 32 provide aninterface between network links and crossconnect 34. The crossconnect 34receives packet streams from the port controllers 32 coupled to theincoming links and selects one of the port controllers coupled to theoutgoing links to transmit the packet stream. The network elementcontroller 36 generates or utilizes management information received bythe packet and exercises overall control of the network element. Thenetwork element controller 36 may also receive from or transmit to theport controllers 32 some or all of the network management informationconveyed by the CDL header.

FIG. 3C illustrates a port controller 32 of an ingress port of an edgenetwork element 26. The port controller 32 includes an optical toelectrical (O/E) converter 38 and a monitor and CDL handler 39. The CDLhandler 39 of the port controller 32 connected to one of the ingresslinks is used to replace the preamble with the CDL header. The portcontroller 32 of a transit network element 28 or transit port of an edgenetwork element 26 includes a CDL handler that is configured to modifythe CDL header of incoming packets with network management informationand forward the packet to a neighboring transit network element toegress network element 26. The port controller 32 of an egress networkelement 26 is shown in FIG. 3D and includes an electrical to opticalconverter 41 which is positioned downstream of the CDL handler 39. TheCDL handler 39 for the egress network element 26 is configured toreplace the CDL header of the incoming packets with the preamble.

FIG. 4 shows a system block diagram of computer system 20 that may beused as a router or host or used to execute software of an embodiment ofthe invention. The computer system 20 includes memory 42 which can beutilized to store and retrieve software programs incorporating computercode that implements aspects of the invention, data for use with theinvention, and the like. Exemplary computer readable storage mediainclude CD-ROM, floppy disk, tape, flash memory, system memory, and harddrive. Additionally, a data signal embodied in a carrier wave (e.g., ina network including the Internet) may be the computer readable storagemedium. Computer system 20 further includes subsystems such as a centralprocessor 40, fixed storage 44 (e.g., hard drive), removable storage 46(e.g., CD-ROM drive), and one or more network interfaces 54. Othercomputer systems suitable for use with the invention may includeadditional or fewer subsystems. For example, computer system 20 mayinclude more than one processor 40 (i.e., a multi-processor system) or acache memory. The computer system 20 may also include a display,keyboard, and mouse (not shown) for use as a host.

The system bus architecture of computer system 20 is represented byarrows 60 in FIG. 4. However, these arrows are only illustrative of onepossible interconnection scheme serving to link the subsystems. Forexample, a local bus may be utilized to connect the central processor 40to the system memory 42. Computer system 20 shown in FIG. 4 is only oneexample of a computer system suitable for use with the invention. Othercomputer architectures having different configurations of subsystems mayalso be utilized. Communication between computers within the network ismade possible with the use of communication protocols, which govern howcomputers exchange information over a network.

In the following description, the term end-to-end refers to OAM&Pinformation that pertains to a specific optical path in its entirety.Preferably, only the source or destination end-point network elementsact upon this information, however, intermediate network elements maygenerate this information. The term hop-by-hop refers to OAM&Pinformation that pertains to the portion of the optical path between twoadjacent network elements. Preferably, only adjacent network elementsact upon this information. CDL information is provided on a per packetbasis and applies to a specific optical path. When a fiber is used tocarry multiple wavelengths, one of the wavelengths may be selected tocarry information that applies collectively to all optical paths. Thisis implemented at a management layer above CDL and is transparent toCDL.

The following describes a packet based optical network that usesEthernet data link layer at speeds, for example, of 10 Gbps and above,both over high speed point-to-point circuits (i.e., dark fiber) and overwavelength division multiplexing (WDM), where multiple optical channelsshare one fiber. However, it is to be understood that the system may beused with media types and different than those described herein, withoutdeparting from the scope of the invention.

As discussed above, CDL is a wrapper around the link layer packet. TheCDL wrapper comprises a self-contained 8 byte CDL header that isprepended to standard Ethernet packets (e.g., IEEE 802.3) by replacing apreamble of the Ethernet packet. Since the Ethernet preamble is also 8bytes in length, the overall size of a CDL modified Ethernet packet isthe same as a standard Ethernet packet. Thus, CDL headers can beinserted into standard Ethernet packets without any change in bandwidth.As further described below, the Ethernet preamble is replaced with theCDL header at a network edge as packets enter the network, and the CDLheader is removed and replaced with the Ethernet preamble at an egressboundary of the network. It is to understand that although the inventionis described herein using an Ethernet packet, other types of packetshaving a preamble may also be used. Thus, the term “Ethernet packet” asused herein includes packets formatted according to standards other thanIEEE 802.3.

FIG. 5 illustrates a summarized version of a standard Ethernet packet 80before the preamble is replaced with the CDL header. The packet 80includes a start of frame field 82, preamble 84, data field 86, and CRC(cyclic redundancy check) 88. Standard IEEE 802.3/Ethernet packetstypically include the following fields after the preamble: destinationaddress (6 bytes), source address (6 bytes), length or type field (2bytes), data field (46–1500 bytes), and frame check sequences (4 bytes).These fields are summarized as the data field 86 in FIG. 5 forsimplification. The destination Ethernet address is the address of theintended receiver. The source Ethernet address is the unique Ethernetaddress of the sending system. The length or type field is the number ofbytes of data or the higher layer protocol identifier. The CDL packetmay be variable in size and CDL implementations preferably provide forEthernet packets from a minimum of 64 bytes to a maximum of 9800 bytes.Short packets are padded to 64 bytes (for IEEE 802.3 frame formats). A32-bit CRC (cyclic redundancy check) is added at the end of the frame toprovide error detection in the case where line errors result incorruption of the frame. Any frame with an invalid CRC is discarded bythe receiver without further processing. The above described fields allremain in the Ethernet packet when the CDL header is added to thepacket. Only the preamble field 84 is removed.

FIG. 6 illustrates the modified Ethernet packet 90 with CDL header 92inserted in place of the preamble 84. The value for the start of frame(or start of packet) field 82 is preferably the same as the value for astandard IEEE 802.3 physical layer. On transmission layers that do notcarry SOF delimiters, the value of SOF is preferably 0x0 and there is adistinct delineation header. The following fields are preferablyincluded in the CDL header 92 (FIG. 6):

-   -   Byte [1]: Packet type and OAM information 98    -   Byte [2]: Message channel 100    -   Byte [3–6]: Application specific information 102    -   Byte [7]: Header cyclic redundancy check (CRC) 104        The following describes the contents and function of each of the        fields in the order listed.

The OAM field 98 carries packet type information, error flags, and anautomatic protection switching (APS) subchannel. Automatic protectionswitching provides the capability of a transmission system to detect afailure on a working facility and to switch to a standby facility torecover the traffic, thus, improving overall system availability. Thetype field identifies whether or not the data and CRC fields 86, 88 arepresent.

-   -   OAM Packet Type Field [7:6]:        -   00: Standard IEEE 802.3/Ethernet packet with CDL header in            place of preamble        -   01: Standard IEEE 802.3/Ethernet packet (with standard            preamble)        -   10: Idle packet with CDL header        -   11: Reserved            The above is a preferred encoding of the Type field. It is            to be understood that other encodings may be used. The Type            field position and encoding is preferably such that a            standard Ethernet frame can be identified.    -   OAM [5]: APS framing BIT        -   0: OAM [4] is a bit in the body of current APS frame        -   1: OAM [4] is an idle bit between APS frames    -   OAM [4]: APS Subchannel. May be a bit of the 16 bit APS frame or        an idle bit between two consecutive APS frames.    -   OAM [3]: End-to-end backward defect indication (BDI-E)    -   OAM [2]: End-to-end forward defect indication (FDI-E)    -   OAM [1]: Hop-by-hop backward defect indication (BDI-H)    -   OAM [0]: Hop-by-hop forward defect indication (FDI-H)        The 16 bit APS frame is constructed out of the OAM [4] bit from        16 consecutive packets. OAM [5] bit is preferably clear in these        packets and set in the packet preceding the first packet and in        the packet following the 16^(th) packet. OAM [5] bit may be set        in more than one packet preceding the first of 16 packets and in        more than one packet following the 16 packets. The set of        fields, code values, and their semantics may be the same as k1        and k2 bytes used in SONET/SDH (ITUTG841) to support line        multiplex section level automatic protection switching:    -   APS [15:13]: Reserved    -   APS [12]: APS architecture    -   APS [11:8]: APS request/status    -   APS [7:4]: APS request channel    -   APS [3:0]: APS bridged channel.

The message channel 100 provides a communication mechanism between thenetwork elements. Messages are preferably transmitted in packets usingHDLC (high level data link control) framing and are transferred 8 bitsat a time. Means for layering higher layer protocols such as IP over anHDLC channel are well known by those skilled in the art. Messages arehop-by-hop and may be forwarded or routed according to establishedrouting protocols. The message channel 100 allows managementcommunication over the same physical facilities as the user data butwithout taking any bandwidth from the user data.

The optical management messages support, in addition to fault indicationand protection switching signaling, connectivity verification,performance monitoring, and processor-to-processor messages.Connectivity verification and performance monitoring are preferablyperformed periodically and handled by hardware or a dedicatedmicrocontroller. Through connectivity verification, a receiver canperiodically ascertain that all the intermediate network elements, as acombined result of initial provisioning and subsequent protectionswitches, are correctly configured so that the optical path terminatingin the receiver originates at the correct network element. Performancemonitoring allows intermediate network elements along an optical path toperiodically communicate to the destination network element variousmetrics of the quality of the optical path to the destination networkelement and to the source network element. The processor-to-processormessages include routing and signaling protocol messages for automaticestablishment of optical paths and management messages which allow thenetwork to be managed.

CDL may provide numerous alarms and error messages that are sent via themessage channel 100 in the CDL header. Alarms, which are also known asdefects or faults, are associated with complete failures. Errors (alsoreferred to as anomalies) pertain to incomplete failures such as parityerrors. Network elements may detect events at various layers (e.g.,section, line, and path) and notify other devices of pending adversenetwork conditions. CDL management facilities enable easytroubleshooting, failure detection, fault isolation, centralizedmaintenance, and remote provisioning.

The side-band message channel 100 provides a mechanism for supportingsingle ended management, as shown in FIG. 7. One node of the network isa network management station 110 used to monitor and control overallnetwork operation. The network management station 110 is connected to afirst network element 112 which is connected through a converged datalink to a second network element 114. The network management station 110can configure, manage, and troubleshoot both network elements 112, 114without requiring a direct link between the network management station110 and the second network element 114. Conventional management systemsoften utilize in-band management communication that mixes managementtraffic in with user data on the link between the network elements,which may lead to security problems. Furthermore, in-band managementcommunication is susceptible to congestion crowding out the managementtraffic.

FIG. 8 illustrates a plurality of network elements 120, 122, 124, 126,128, 130 and a network management station 132 connected to networkelement 130. The CDL message channel 100 allows network elements 122 and124 to send alarm messages indicating that link 134 between the networkelements has failed to the network management station 132. The messagechannel 100 provides a secure means of forwarding the message which isnot affected by congestion of user traffic.

As long as network elements that transmit, modify, and terminate CDLalong an optical path are secure, the operation of CDL is secure. Inorder for security to be maintained, any network element that connectsto an untrusted port terminates the CDL optical path.

The application specific (AS) field 102 carries information between endnodes that is forwarded along an optical path. Preferably, theinformation is not modified by an intermediate network element along theoptical path. The application specific field 102 may include asubinterface identifier to assist in multiplexing packet streams asshown in FIGS. 9A and 9B, for example. FIG. 9A shows a CDL header 139configured to support multiplexing of packet streams. The headerincludes a subinterface identifier 212. The bytes are preferablytransmitted in ascending order. If a field is multiple bytes long, themost significant bits are transmitted first. At the transmitting node140, multiple lower rate packet streams are multiplexed into anaggregate packet stream (FIG. 9B). To facilitate demultiplexing at thereceiving end 142, the least significant application specific bytecarries an 8-bit subinterface identifier. The identifier allows trafficfrom multiple ports to be combined and remain distinct from one anotherby labeling the ports to keep the traffic separate. The identifier isused to demulitplex the packet streams when they reach their destinationor receiving node 142. As shown in FIG. 9B, individual packets 144, 146,148, 150 are labeled A, B, C, D so that packets from different ports canbe sent together on a common trunk. The label identifies the port onwhich the packet originated (e.g., packet 144 is on port A, packet 146is on port B, packet 148 is on port C, and packet 150 is on port D). Thesubinterface identifier is included in the header added to the packet atnetwork element 140. Network element 142 removes the CDL header andsends each packet to its corresponding destination port (A-D). Since theidentifier field is inserted into the field previously occupied by thepreamble, it does not interfere with wire speed performance or affectintegrity of the payload.

The application specific field 102 may also be used to supportapplications other than multiplexing. For example, the applicationspecific field 102 may be used to facilitate multi-protocol labelswitched routing.

The header CRC 104 is employed for header error protection and coversthe CDL header but not any other parts of the frame. The CRC ispreferably computed over the entire value of the CDL header, includingthe AS field 102, but excluding the value of the SOF field 82. The CRCmay be based on CRC-8 [ITU-T G.432.1]. For example, the CRC header maybe an 8-bit sequence that is the remainder of the modulo-2 division bythe generator polynomial x^8+x^2+x+1 of the product x^8 multiplied bythe content of the CDL header excluding the header CRC. The 48-bit longrelevant portion of the CDL header is taken to represent a polynomial oforder 47. The coefficients can have the value 0 or 1. The first bit ofthe header represents the coefficient of the highest order (x^47) term.The polynomial operations are performed modulo-2. The CRC header ispreferably recomputed whenever any of the fields in the header arechanged and passed transparently whenever the fields of the header donot change.

FIG. 10 shows an example of a linear feedback shift register that may beused to calculate the 8-bit CRC in a bit serial fashion. 8, 16, or 32parallel implementations can be deduced from the bit serialimplementation. As is well known by those skilled in the art, a feedbackshift register implements long division if coefficients of the dividendare applied at the input on the right. When all the dividend bits havebeen shifted in, the value stored in the shift register is theremainder. It is to be understood that other methods may be used tocalculate 110 the CRC, without departing from the scope of theinvention.

Idle packets may be inserted into a transmit packet stream if thecorresponding receive packet stream has long idle intervals, as shown inFIG. 11A. FIG. 11A shows three packets 162, 164, 168 entering an opticalnetwork 170. There is a space between packets 162 and 164 representing alocation in time when no user data is received. As shown in FIG. 11B, anidle packet 160 is inserted between packets 162 and 164 so that OAM&Pinformation can be transmitted even when there is no user data beingtransmitted. The idle packet 160 includes the start of field indicator82, OAM field 98, message channel 100, application specific field 102,and a header CRC 104, as described above and shown in FIG. 6. The idlepacket 160, however, does not include the Ethernet packet payload (i.e.,data 86 and CRC 88). When idle packet 160 is inserted, the minimumtransmit IPG (InterPacket Gap) constraint is preferably observed.Furthermore, when back-to-back idle packets 160 are transmitted,preferably a minimum of (2×Minimum Transmit IPG+Shortest Legal MACFrame) spacing separates an idle packet from the immediately followingidle packet.

FIG. 12 illustrates an optical transport network comprising a pluralityof network elements 170 configured to provide two separate optical pathsA, B between network elements 172, 174 located along an edge of theoptical network. The edge of the network is associated with trafficaggregation or distribution. It is also typically the point ofconvergence of regional traffic housed in facilities referred to asnetwork points of presence (POPs). As shown in FIG. 12, Ethernet packets80 are received at network element 172. The Ethernet preamble isstripped from packet 80 at network element 172 and the CDL header isinserted in place of the preamble. The modified packets 90 are providedwith two paths to provide redundancy in case of a failure along one ofthe paths. For example, if a failure is identified on path A, thepackets will be transmitted to the network element 174 through path B.Once the packets reach network element 174, the CDL header is removedand replaced with the Ethernet preamble.

FIG. 13 illustrates an optical network with a plurality of networkelements 180 arranged in a dual ring topology. The ring consists of acollection of ring interfaces connected by point-to-point lines 182. Oneadvantage of the ring topology is its survivability. For example, if afiber cable is cut, the multiplexers have the local intelligence to sendthe services affected via an alternate path through the ring without alengthy interruption. The preamble is stripped from the packet and theCDL header is added as the packet enters any one of the network elements180 located within the ring. A CDL header 200 for use with a networkhaving a ring topology is shown in FIG. 14. In addition to the OAM field98, message channel 100, and header CRC 104, the header includes thefollowing fields:

-   -   TTL: Time To Live 202    -   R: Ring Identifier 204    -   Pri: Priority 206    -   D: Destination strip 208    -   Usage: Usage 210    -   SII: Sub-Interface identifier 212.        These fields correspond generally to the SRP (spatial reuse        protocol) for use with ring based media, as described in The        Cisco SRP MAC Layer Protocol, dated May 1, 2000, published in        the Internet Draft of the Internet Engineering Task Force        (IETF).

A mesh topology network is shown in FIG. 15. As described with respectto FIG. 12, the CDL headers 92 are added and removed at the networkedge. The network includes three paths between network elements 220 and222. A failure was detected along path A (as indicated by an x) and CDLdetect indications caused rerouting so the packets were switched totravel along path B to network element 222.

FIGS. 16A–16C illustrate a network element 230 located within an opticaltransport system 232. The network element 230 receives two sets ofidentical packets from path A and redundant path B. Defect indicationprovided by the message channel 100 or by end-to-end forward defectindication (FDI-E) allows the receiving node 230 to switch to theredundant channel if a failure threshold is exceeded. FIG. 16Billustrates the transport of packets B1–B4 by the network element 230.During the transmission, an error was detected in packets B2 and B4. Thesecond error presented by packet B4 resulted in the error threshold ofnetwork element 230 being reached. After B4 passed through networkelement 230, the network element switched to the packets received frompath A and transmitted packet A5 in place of packet B5, as shown in FIG.16C. Packets A1–A4 and B5 are discarded by the network element 230.

FIG. 17 is a flowchart illustrating a process for modifying an Ethernetpacket to provide OAM&P capabilities. The Ethernet packet is transmittedto a network element located on an edge of the optical network at step250. The Ethernet preamble is removed (step 252) and the CDL header isinserted (step 254). The modified packet is then transmitted through thenetwork (step 256). When the packet is received by a network elementlocated at an egress boundary of the network (step 257), the CDL headeris removed (step 258) and the Ethernet preamble is replaced (step 260).

As described above, the preferred embodiment of the present invention isimplemented in a packet over optics network. However, as one skilled inthe relevant art would find apparent, the present invention may beimplemented to operate with other carrier technologies. Furthermore, thenetwork may be any type of network appropriate for a given application.For example, the network may be a large public wide area carriertransport system, a private wide area network (WAN), or local areanetwork (LAN).

WAN links may be provisioned as point-to-point circuits over carriernetworks with the circuits dropped off from ADMs via CDL interfaces. CDLinterfaces for network connectivity include core (i.e., backboneinfrastructure for interconnecting distribution or aggregating points ina large network), edge (i.e., data transport between customer premisesand points of presence (POPs) and intra-POP connectivity), and metro(i.e., interbuilding connections such as in a small city downtown areaor university campus) applications.

As can be observed from the foregoing, CDL introduces no overheadrelative to standard Ethernet packets. Furthermore, CDL may support datarates of over 40 Gbps and higher for future network systems. CDLeliminates the SONET/SDH overhead, termination, and equipment, thusproviding substantial savings in equipment and operational costs.Moreover, CDL allows integrated network OAM&P in that one connection canreach all network elements within a given architecture and separatelinks are not required for each network element. Remote provisioningprovides centralized maintenance and reduced travel for maintenancepersonnel. Substantial overhead information is provided in CDL to allowquicker troubleshooting and detection of failures before they degrade toserious levels.

Although the present invention has been described in accordance with theembodiments shown, one of ordinary skill in the art will readilyrecognize that there could be variations made to the embodiments withoutdeparting from the scope of the present invention. Accordingly, it isintended that all matter contained in the above description and shown inthe accompanying drawings shall be interpreted as illustrative and notin a limiting sense.

1. A method for conveying network management information within anetwork, the method comprising: receiving an Ethernet packet at anetwork element; modifying the Ethernet packet by inserting a header inplace of the preamble within the packet while maintaining the format ofthe Ethernet packet, said header configured to provide support fornetwork management; transmitting the modified packet from the networkelement; transmitting a defect indicator within said header; andswitching a receiving node to a backup path.
 2. The method of claim 1wherein the network element is in communication with an optical network.3. The method of claim 1 wherein said network management includesoperations, administration, and maintenance.
 4. The method of claim 3wherein the header comprises an operations, administration, andmaintenance channel and further comprising transmitting operations,administration, and maintenance information from the network element toa network management station.
 5. The method of claim 3 wherein theheader comprises an operations, administration, and maintenance channeland further comprising transmitting operations, administration, andmaintenance information from the network element to other networkelements.
 6. The method of claim 3 wherein said network managementfurther includes provisioning of paths within the network.
 7. The methodof claim 3 wherein said network management further includes performancemonitoring of paths within the network.
 8. A method for conveyingnetwork management information within a network, the method comprising:receiving an Ethernet packet at a network element; modifying theEthernet packet by inserting a header in place of the preamble withinthe packet while maintaining the format of the Ethernet packet, saidheader configured to provide support for network management;transmitting the modified packet from the network element; and providingan automatic protection switching subchannel within said header.
 9. Themethod of claim 8 wherein said header includes the same number or afewer number of bytes than the preamble of the Ethernet packet so thatthe size of the packet is not increased when the preamble is replaced bythe header.
 10. The method of claim 9 wherein said header comprises 8bytes.
 11. The method of claim 8 wherein said header includes a messagechannel.
 12. The method of claim 11 further comprising using HDLC on themessage channel.
 13. A method for conveying network managementinformation within a network comprising a plurality of network elements,the method comprising: receiving an Ethernet packet at a networkelement; modifying the Ethernet packet by inserting a header in place ofthe preamble within the packet while maintaining the format of theEthernet packet, said header configured to provide support for networkmanagement; transmitting the modified packet from the network element;and communicating routing table information among said plurality ofnetwork elements via said header.
 14. The method of claim 13 whereinsaid header includes packet type information.
 15. The method of claim 14wherein the packet type information identifies whether the packet is anidle packet or a data packet.
 16. The method of claim 14 wherein thepacket type information identifies that the Ethernet packet has beenmodified.
 17. The method of claim 13 further comprising providingsideband communication within the network via a sideband channel. 18.The method of claim 17 further comprising IP routing over the sidebandchannel to enable communication of management data.
 19. The method ofclaim 17 further comprising using the sideband channel to performtopology discovery.
 20. The method of claim 13 further comprisingmultiplexing packet streams at the network element.
 21. The method ofclaim 20 wherein said header comprises a subinterface identifier whichidentifies an originating port for each of the packets.
 22. The methodof claim 20 further comprising demultiplexing the packet streams at areceiving node.
 23. The method of claim 13 further comprising a networkmanagement station and wherein the management station has access to saidplurality of network elements via said header.
 24. The method of claim13 wherein the network element is in communication with at least onerouter.
 25. A method for supporting management of a network, the methodcomprising: receiving a modified Ethernet packet at a network element,the modified packet comprising a header configured to provide supportfor operations, administration, and maintenance; replacing the header inthe modified packet with a preamble within the packet to create anEthernet packet; and transmitting the Ethernet packet from the networkelement; wherein the header is the same size as the preamble.
 26. Themethod of claim 25 wherein said header includes an error-detecting codeword to detect errors in the header.
 27. The method of claim 26 whereinsaid error detecting code is a cyclic redundancy check field.
 28. Themethod of claim 25 wherein the network element is located at an egressboundary of the network.
 29. The method of claim 25 wherein receiving amodified Ethernet packet comprises receiving the modified packet from atransit network element located within the network.
 30. The method ofclaim 29 wherein the network element is in communication with an opticalnetwork.
 31. The method of claim 25 wherein the network is a WAN. 32.The method of claim 25 wherein transmitting the Ethernet packetcomprises transmitting the Ethernet packet without a SONET frame. 33.The method of claim 25 wherein transmitting the Ethernet packetcomprises transmitting the Ethernet packet without SONET overhead. 34.The method of claim 25 wherein replacing the header comprisesmaintaining a minimum interpacket gap.
 35. The method of claim 25wherein replacing the header in the modified packet comprisesmaintaining the format of the Ethernet packet.
 36. An Ethernet networksystem for conveying network management information, the system having anetwork element comprising: a port controller operable to receive anEthernet packet, modify the Ethernet packet by inserting a header inplace of the preamble within the packet while maintaining the format ofthe Ethernet packet, said header configured to provide support fornetwork management, the port controller comprising an optical toelectrical converter and a CDL handler operable to insert the headerinto the packet; and a network element controller coupled to the portcontroller and operable to generate and consume network managementinformation; wherein the header comprises: an operations,administration, and maintenance field: a message channel; an applicationspecific field; and a header error detection field.
 37. The system ofclaim 36 further comprising a crossconnect configured to receive thepacket from the port controller and select an egress port controller totransmit the packet from the network element.
 38. The system of claim 36further comprising a second network element positioned at an egressboundary of the network, the second network element comprising: a portcontroller operable to receive the modified packet and replace theheader with the preamble; and a network element controller coupled tothe port controller of the second network element and operable togenerate and consume network management information.
 39. The system ofclaim 38 wherein the second network element is a downstream networkelement and further comprising a transit network element operable toreceive the modified packet, modify the header, and forward the packetto the second network element.
 40. The system of claim 36 wherein theport controller and the network element are configured for receiving andsending Ethernet packets frames.
 41. An Ethernet network system forconveying network management information, the system having a networkelement comprising: a port controller operable to receive an Ethernetpacket, modify the Ethernet packet by inserting a header in place of thepreamble within the packet while maintaining the format of the Ethernetpacket, said header configured to provide support for network managementand comprising an operations, administration and maintenance field, theport controller comprising a CDL handler and an electrical to opticalconverter; and a network element controller coupled to the portcontroller and operable to generate and consume network managementinformation.
 42. A computer program product for conveying networkmanagement information within a network comprising a plurality ofnetwork elements, the product comprising: code that modifies an Ethernetpacket by inserting a header in place of the Ethernet preamble withinthe packet while maintaining the format of the Ethernet packet, saidheader providing support for network management; code that transmits themodified packet from a network element; code that communicates routingtable information among said plurality of network elements via saidheader; and a computer-readable storage medium for storing the codes;wherein the computer-readable storage medium is not a data signalembodied in a carrier wave.
 43. The computer program product of claim 42further comprising code that removes said header from the modifiedpacket and replaces the preamble.
 44. The computer program product ofclaim 42 further comprising code that provides sideband communicationwithin the network.
 45. The computer program product of claim 42 furthercomprising code that provides each of the packets with a subinterfaceidentifier within said header to allow multiplexing of packet streams.46. The computer program product of claim 42 wherein code that maintainsthe format of the Ethernet packet comprises code that maintains aninterpacket gap.
 47. A system for conveying network managementinformation in an Ethernet system comprising a plurality of networkelements, the system comprising: means for receiving an Ethernet packetat a network element; means for modifying of the Ethernet packet byinserting a header in place of the preamble within the packet whilemaintaining the format of the Ethernet packet, said header configured toprovide support for network management; means for transmitting themodified Ethernet packet; and means for communicating routing tableinformation among said plurality of network elements via said header.48. The system of claim 47 wherein means for modifying the packetcomprises hardware.
 49. The system of claim 47 wherein means formodifying the packet comprises microcode.
 50. The system of claim 47wherein means for modifying the packet comprises software.
 51. Thesystem of claim 47 wherein means for modifying the packet comprisesphotonic logic.
 52. The system of claim 47 wherein the network elementis located at an ingress boundary of the network.
 53. The system ofclaim 52 wherein said means for modifying the preamble comprises meansfor replacing an Ethernet preamble with a CDL header.
 54. The system ofclaim 47 wherein the network element is located at an egress boundary ofthe network.
 55. The system of claim 47 wherein said means for modifyingthe preamble comprises means for replacing a CDL header with an Ethernetpreamble.
 56. The system of claim 47 wherein the network element is atransit network element.
 57. A method for supporting management of anetwork, the method comprising: receiving a modified Ethernet packet ata network element, the modified packet comprising a header configured toprovide support for network management; replacing the header in themodified packet with a preamble within the packet to create an Ethernetpacket; transmitting the Ethernet packet from the network element; andtransmitting back-to-back idle packets and separating the idle packetswith a spacing equal to at least two times the minimum transmitinterpacket gap.
 58. An apparatus for conveying network managementinformation within a network comprising a plurality of network elements,comprising: means for receiving an Ethernet packet at a network element;means for modifying the Ethernet packet by inserting a header in placeof the preamble within the packet while maintaining the format of theEthernet packet, said header configured to provide support for networkmanagement; means for transmitting the modified packet from the networkelement; and means for communicating routing table information amongsaid plurality of network elements via said header.